1. Field of the Invention
The present invention relates to a disk drive apparatus comprising recording media to be rotated, such as magnetic disks or optical disks.
2. Description of the Related Art
In general, a magnetic disk drive apparatus (to be referred to as an HDD hereinafter) of 2.5 inches, for example, comprises a mechanical section, and a printed circuit board mounted with a control circuit for controlling the operation of a read/write circuit and the mechanical section. The mechanical section includes magnetic disks, a spindle motor, a disk clamp for fixing the magnetic disks to the spindle motor, magnetic heads, a carriage, a carriage drive motor (voice coil motor), and the like. The printed circuit board is electrically connected to the magnetic heads, spindle motor, and voice coil motor of the mechanical section.
Generally, the magnetic disks are fitted on the spindle motor as follows. Specifically, on the spindle motor is provided a cylindrical hub having a flange on one of its ends. The hub is rotated by the spindle motor. A plurality of magnetic disks and ring-shaped spacers are alternately stacked on the flange, and the disk clamp is fixed to the other end of the hub by a screw. The disk clamp has elasticity and therefore generates a biasing force for urging the magnetic disks and the spacers against the flange. By this force, the magnetic disks are fixed to and held by the hub of the spindle motor.
In a HDD having only one magnetic disk, a spacer may be arranged between the disk and the clamp or between the disk and the flange of the hub.
With the HDD having the above-mentioned arrangement, upon reading or writing data with respect to the disk, the disk is rotated by the spindle motor and the magnetic head is positioned over one of data tracks concentrically formed on the disk by the carriage. Then, the magnetic head reads data from or writes data on the data track. As a head positioning control system which determines the data read/write performance, there is known a servo-surface servo system (Dedicated Servo System) wherein one surface of a disk is recorded with servo data and used as a servo surface and a data-surface servo system (e.g. Sector Servo System) wherein servo data written on the data tracks on the data surface of a disk are available.
The servo-surface servo system requires a magnetic head for reading servo data and a magnetic head for reading/writing data and therefore has a problem of misalignment between these two magnetic heads resulting from the difference in thermal expansion between the heads with changes in temperature.
The data-surface servo system requires no servo magnetic head and hence does not cause the above problem. In addition, even if misalignment of the magnetic head with respect to the data tracks on the disk is caused by thermal expansion, this misalignment can be eliminated by performing position control for the magnetic head.
If a sudden vibration occurs in the magnetic disk, however, the tracking properties of the magnetic head with respect to the data track on the disk decrease, reducing the positional precision of the head with respect to the data track and varying the flying amount of the magnetic head from the disk. As a result, the data read/write operation becomes unstable to readily cause errors. Specifically, when a sudden vibration of the disk occurs during writing data on the disk by means of the magnetic head, data is written on an incorrect position on the disk. In this case, the incorrectly written data can not be read out by the head.
In many cases, a cause of the occurrence of such a sudden vibration in the disk is the differences in thermal expansion coefficients between a plurality of members used in the disk fixing section. Specifically, the disk fixing section includes, e.g., the magnetic disks themselves, the hub, the spacers, and the disk clamp, and, if the thermal expansion coefficients of these members differ from one another, the differences occur in the quantity of thermal expansion when an environmental temperature changes. The result is a strain occurring in each member. When the differences between the quantities of thermal deformation of the two adjacent members exceed the allowable thermal strain, relative displacement occurs between the two members so as to release the thermal strain in each member, and consequently the disks vibrate.
The above problem may be eliminated by using members having the same thermal expansion coefficient. As an example, U.S. Pat. No. 4,814,652 discloses a technique wherein a motor hub and disks are formed of materials having equal thermal expansion coefficients. In practice, however, in order for the individual members to achieve their respective predetermined functions, it is necessary to select materials meeting these functions, and this makes it difficult to select materials with thermal expansion coefficients equal to one another. In particular, it is extremely difficult to form all members that constitute the disk fixing section by using materials having the same thermal expansion coefficient.